1. Field of the Invention
The present invention relates to an image forming apparatus, such as a copier, a printer, a facsimile machine, a plotter, a multifunctional device capable of performing several of the foregoing functions, or the like, and more specifically, to an image forming apparatus capable of outputting both a sheet subjected to post-processing and a sheet not subjected to post-processing to a so-called housing-internal space formed within the space occupied by the body of the image forming apparatus.
2. Description of the Background
Image forming apparatuses are used as copiers, printers, facsimile machines, and multi-functional devices combining several of the foregoing capabilities.
In a conventional image forming apparatus of a housing-internal output type, an upper face of an apparatus body is formed as a sheet stack portion to stack a sheet on which an image is formed, and a scanner serving as an image reading unit is provided above the sheet stack portion.
In the conventional image forming apparatus the sheet stack portion serving as an output tray portion is located within the space occupied by the body of the image forming apparatus, providing advantages such as a reduction in the size of the apparatus when the apparatus is set up. More specifically, the scanner is located relative to the sheet stack portion so that the space between the scanner and the sheet stack portion is as small as possible. Such a configuration reduces the height of the image forming apparatus, resulting in downsizing the apparatus as a whole.
In recent years, demand has arisen for such a housing-internal output-type image forming apparatus with a post-processing function, and some image forming apparatuses having such a function have been proposed.
For example, one conventional image forming apparatus includes a post-processing unit within a housing-internal space, to which a bundle of sheets bound by post processing is output.
Another conventional image forming apparatus includes a post-processing unit within a housing-internal space, in which a bundle of sheets bound by post-processing is output to a sheet output tray and a sheet not subjected to post-processing is output to a separated sheet output tray.
In still another conventional image forming apparatus, a post-processing tray is substantially vertically disposed alongside a scanner above a sheet output portion of an apparatus body, and a bundle of sheets bound by post-processing is output to a housing-internal space.
For those configurations in which the post-processing unit is located within the housing-internal space, the image reading unit is located all the higher for the post-processing unit, preventing the housing-internal space from being efficiently used as the sheet output space.
For one of the above-described conventional image forming apparatuses, the height of the image forming apparatus as a whole may be relatively high and, among sheets stacked on the sheet stack portion, the image side of a sheet subjected to post-processing may differ from that of a sheet not subjected to post-processing.
Further, when a plurality of sheets is stacked on the post-processing tray, a precedent sheet may need to pass through a sheet reverse unit before a subsequent sheet is fed, resulting in a reduction in productivity.
Also, there is increasing demand for a post-processing unit capable of performing a plurality of types of post-processing operations, such as staple binding, punching, seal stamp, and sorting, and a conventional image forming apparatus has a configuration in which such a post-processing unit is mounted at a lateral side of the apparatus body.
Another conventional image forming apparatus having a common output tray provided at a post-processing unit executes a control method when an interrupt request for image formation not including post-processing is received during execution of image formation including post-processing. In this control method, a plurality of sheets for the interrupted image formation including post-processing held at a staple unit during execution of the image formation not including post-processing.
However, according to the conventional control method, when image formation including post-processing is interrupted by image formation not including post-processing, some sheets for the interrupted image formation including post-processing are held at a sheet alignment portion of the post-processing unit until the interrupt processing is completed. Since there is a certain distance between the sheet alignment position and a housing-internal tray, the restart of interrupted processing is delayed by the distance, resulting in a reduction in productivity.
In another conventional control method that assumes there is a plurality of trays, interrupting image formation not including post is executed in parallel with processing and interrupted image formation including post-processing, and respective sheets are output to separate trays. However, if the conventional control method is used in an image forming apparatus with a single output tray, a sheet output by one image formation may prevent a sheet output by the other image formation, resulting in sheet jam.